Many gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps that draw fuel from the tank and deliver pressurized fuel to the fuel manifolds in the engine combustor via a main supply line. The main supply line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include, for example, a main metering valve and a pressurizing-and-shutoff valve downstream of the main metering valve. In addition to the main supply line, many fuel supply systems also include a bypass flow line connected upstream of the metering valve that bypasses a portion of the fuel flowing in the main supply line back to the inlet of the one or more pumps, via a bypass valve. The position of the bypass valve is typically controlled by a head regulation scheme to maintain a substantially fixed differential pressure across the main metering valve.
The above-described fuel supply system is generally safe, reliable, and robust. Nonetheless, it can suffer certain drawbacks. For example, the metering valve and bypass valve can add to overall system weight and complexity. Moreover, control of the metering valve and bypass valve can result in increased system complexity and cost. Thus, in recent years there has been a desire to implement more electric fuel controls by, for example, controlling the speed of a fuel metering pump. Yet, efforts to implement electric fuel controls have been impeded by the increased cost and complexity of the proposed systems. For example, the need to accurately predict the flow of the fuel metering pump from its speed, regardless of various operating conditions such as, for example, pump performance, fuel viscosity, and output pressure, may rely on relatively complex and costly control schemes.
Hence, there is a need for a system and method of accurately supplying fuel flow to a gas turbine engine regardless of variations in operating conditions, and/or without relying on numerous sensors for sensing the operating conditions, and/or without relying on relatively complex and costly control schemes. The present invention addresses one or more of these needs.